Repurposing melatonin's therapeutic potential in Wilson disease: Addressing copper overload and redox imbalance

Loss-of-function mutations in copper-ATPase ATP7B underlie Wilson disease (WD), a disorder characterized by hepatic copper accumulation and severe hepato-neuropathology. Existing chelation therapeutics remove excess copper but lack intrinsic antioxidant capacity and frequently cause systemic toxicity. Here we evaluate melatonin, an FDA-approved indoleamine with antioxidant and putative metal-chelating activity, as a candidate therapeutic for WD. In ATP7B^-/- hepatocytes, melatonin restored copper-induced reactive oxygen species (ROS) to basal levels, reduced apoptosis twofold, and attenuated Nrf2 nuclear translocation leading to reduction of Hemoxygenase-1 abundance. Live-cell ratiometric analysis of GSSG/GSH using GRX1-roGFP2 expressed in melatonin-treated ATP7B^-/- hepatocytes revealed a significant reduction in intensity-ratio, indicating an effective mitigation of copper-induced glutathione oxidation. Isothermal calorimetric titration revealed a moderate Cu²⁺ affinity (K_a^ITC = 4.54 × 10³ M^-1), yet melatonin produced a stronger reduction in cellular oxidative stress than either d-penicillamine or N-acetylcysteine, underscoring its cooperative antioxidant-chelation advantage. Melatonin (MLT) copper chelation was also rationalized by MD-simulations and DFT framework showing thermodynamically favourable interaction via amide-Cu²⁺ coordination. In-cellulo studies also revealed that copper-induced vesicularized ATP7B reinstates to Golgi in melatonin-treated hepatocytes. In vivo, melatonin treatment reduced copper-induced oxidative stress in zebrafish embryos and lowered copper burden in Caenorhabditis elegans WD model. Our studies revealed that encapsulation of melatonin within an engineered polymeric nanocapsules having dithiol linkers, susceptible to cleavage by GSH, extended melatonin's circulatory half-life ten-fold and enhanced its ROS-scavenging efficacy three-fold relative to free melatonin. This work introduces a unique dual-function therapeutic strategy that integrates antioxidant activity with copper chelation, simultaneously addressing copper overload and redox imbalance. Repurposing melatonin, with its established clinical safety, offers rapid and cost-effective translational pathway toward WD-therapy while providing a generalizable platform for redox- and metal-associated disorders.